9-21970951-GC-G

Position:

• chr9-21970951-GC-G

Variant summary

Our verdict is Likely pathogenic. Variant got 6 ACMG points: 6P and 0B. PVS1_Strong PM2

The ENST00000304494.10(CDKN2A):​c.407delG​(p.Gly136fs) variant causes a frameshift change involving the alteration of a non-conserved nucleotide. The variant allele was found at a frequency of 0.000000685 in 1,459,564 control chromosomes in the GnomAD database, with no homozygous occurrence. Variant has been reported in ClinVar as Uncertain significance (★★). Synonymous variant affecting the same amino acid position (i.e. G136G) has been classified as Likely benign.

• Frequency:
  • Genomes: not found (cov: 32)
  • Exomes 𝑓: 6.9e-7 (0 hom.)
• Consequence: CDKN2A ENST00000304494.10 frameshift
• Clinical Significance: Uncertain significance criteria provided, multiple submitters, no conflicts U:3
• Conservation: PhyloP100: -1.99

Genes affected

CDKN2A (HGNC:1787): (cyclin dependent kinase inhibitor 2A) This gene generates several transcript variants which differ in their first exons. At least three alternatively spliced variants encoding distinct proteins have been reported, two of which encode structurally related isoforms known to function as inhibitors of CDK4 kinase. The remaining transcript includes an alternate first exon located 20 Kb upstream of the remainder of the gene; this transcript contains an alternate open reading frame (ARF) that specifies a protein which is structurally unrelated to the products of the other variants. This ARF product functions as a stabilizer of the tumor suppressor protein p53 as it can interact with, and sequester, the E3 ubiquitin-protein ligase MDM2, a protein responsible for the degradation of p53. In spite of the structural and functional differences, the CDK inhibitor isoforms and the ARF product encoded by this gene, through the regulatory roles of CDK4 and p53 in cell cycle G1 progression, share a common functionality in cell cycle G1 control. This gene is frequently mutated or deleted in a wide variety of tumors, and is known to be an important tumor suppressor gene. [provided by RefSeq, Sep 2012]

CDKN2A (HGNC:):

ACMG classification

Verdict is Likely_pathogenic. Variant got 6 ACMG points.

• PVS1: Loss of function variant, product does not undergo nonsense mediated mRNA decay. Variant is located in the 3'-most 50 bp of the penultimate exon, not predicted to undergo nonsense mediated mRNA decay. Fraction of 0.136 CDS is truncated, and there are 2 pathogenic variants in the truncated region.
• PM2: Very rare variant in population databases, with high coverage

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
CDKN2A	NM_000077.5	c.407delG	p.Gly136fs	frameshift_variant	2/3	ENST00000304494.10	NP_000068.1
CDKN2A	NM_058195.4	c.*51delG		3_prime_UTR_variant	2/3	ENST00000579755.2	NP_478102.2

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
CDKN2A	ENST00000304494.10	c.407delG	p.Gly136fs	frameshift_variant	2/3	1	NM_000077.5	ENSP00000307101.5
CDKN2A	ENST00000579755	c.*51delG		3_prime_UTR_variant	2/3	1	NM_058195.4	ENSP00000462950.1

Frequencies

GnomAD3 genomes Cov.: 32

GnomAD4 exome AF: 6.85e-7 AC: 1 AN: 1459564 Hom.: 0 Cov.: 31 AF XY: 0.00000138 AC XY: 1 AN XY: 726162

Gnomad4 AFR exome AF: 0.00

Gnomad4 AMR exome AF: 0.00

Gnomad4 ASJ exome AF: 0.00

Gnomad4 EAS exome AF: 0.00

Gnomad4 SAS exome AF: 0.00

Gnomad4 FIN exome AF: 0.0000193

Gnomad4 NFE exome AF: 0.00

Gnomad4 OTH exome AF: 0.00

GnomAD4 genome Cov.: 32

Bravo AF: 0.00000378

ClinVar

Significance: Uncertain significance

Submissions summary: Uncertain:3

Revision: criteria provided, multiple submitters, no conflicts

Submissions by phenotype

Hereditary cancer-predisposing syndrome Uncertain:2

Uncertain significance, criteria provided, single submitter	clinical testing	Color Diagnostics, LLC DBA Color Health	Apr 17, 2020	This variant deletes 1 nucleotide in exon 2 of the CDKN2A (p16INK4A) gene, creating a frameshift and premature translation stop signal. This variant is not expected to trigger nonsense-mediated decay, and it is predicted to truncate the C-terminus of the ankyrin repeat domain. Truncation variants that delete the ankyrin repeat domain and are reported as disease-causing in ClinVar all impact conserved motifs in the ankyrin repeat (ClinVar variation ID: 216035, 406710, 463500, 463503, 573002). However, this variant truncates the protein after the last conserved motif (PMID: 8880901, 12519945). To our knowledge, functional studies have not been performed for this variant nor has this variant been reported in individuals affected with hereditary cancer in the literature. This variant has not been identified in the general population by the Genome Aggregation Database (gnomAD). Loss of CDKN2A function is a known mechanism of disease (clinicalgenome.org). The available evidence is insufficient to determine the role of this variant in disease conclusively. Therefore, this variant is classified as a Variant of Uncertain Significance. -
Uncertain significance, criteria provided, single submitter	clinical testing	Ambry Genetics	Nov 24, 2018	The c.407delG variant, located in coding exon 2 of the CDKN2A gene, results from a deletion of one nucleotide at nucleotide position 407, causing a translational frameshift with a predicted alternate stop codon (p.G136Afs*10). Frameshifts are typically deleterious in nature, however, this frameshift occurs at the 3' terminus of CDKN2A, is not expected to trigger nonsense-mediated mRNA decay, and impacts only the last 21 amino acids of the protein. The exact functional impact of these altered amino acids is unknown at this time. Since supporting evidence is limited at this time, the clinical significance of this alteration remains unclear. -

Familial melanoma Uncertain:1

Uncertain significance, criteria provided, single submitter

clinical testing

Labcorp Genetics (formerly Invitae), Labcorp

Mar 09, 2020

This variant has not been reported in the literature in individuals with CDKN2A (p16INK4a)-related conditions. This variant is not present in population databases (ExAC no frequency). This sequence change results in a premature translational stop signal in the CDKN2A (p16INK4a) gene (p.Gly136Alafs*10). While this is not anticipated to result in nonsense mediated decay, it is expected to disrupt the last 21 amino acids of the CDKN2A (p16INK4a) protein. Experimental studies and prediction algorithms are not available or were not evaluated, and the functional significance of this variant is currently unknown. In summary, the available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance. -

Computational scores

Source: dbNSFP v4.3

Splicing

Name	Calibrated prediction	Score	Prediction
SpliceAI score (max)		0.020		Details are displayed if max score is > 0.2

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

LitVar

Other links and lift over

dbSNP: rs749588877; hg19: chr9-21970950;